Variable-resistance device



PATENr-i orrics.'f

' Join; PARKIN,I .13.,- or SAN RAFAELLCALIFORNIA.

' VARIABLE-RESISTANCE DEVICE.

. and useful VariablerResista-nce' Device, of

" provide a durable'high resistance element.

which the following is a specification.

The invention relates to variable resistance devices for use asrheostats and potent ometers. An object of the invention is to provide avariable resistance device which is not sub jected to wearand which maybe readily manipulated to vary resistance within the limits of itscapacity. f g Another object of the invention is to pro.-' vide a simpleand cheap variable resistance device, which is particularly adapted tohandle small currents. A further object of the invention is Theinvention possesses other advantageous features, some of which, with theforegoing, will be set forth at length in the following description,where I shall outlinein full that form of the invention which I haveselected for illustration in the drawings accompanying and forming partof the present specification, In said drawings I have shown two, formsof the device of my invention, but it is to be understood that'l do notlimit myself to such forms, since the invention, as expressed in theclaims, may be embodied in other forms. Referring to said drawings:Figure 1 is a rear elevation of one form of device of my invention, partthereof being shown in section to disclose the con- 'struction. r

Fig. 2 is a side elevation of the device shown in Fig. 1, mounted on apanel.

Fig. 3 is a rear elevation, partly in section of a modified form-of thedevice.

The device of my invention is primarily adapted for handling smallcurrents, but it may be constructed tohandle larger currents. whendesired. It is particularly adapted for use as a rheostat or apotentiometer, and finds utility in radio signaling apparatus, as apotentiometer for varying the plate potential in a vacuum tube or as agrid leak for a vacuum tube, or in other uses. lVhile its constructionrenders it particularly adaptable for use in radio signaling apparatus,its utility is not confined to such, but it ay be employed in allinstances where it is desired to vary 1919. Serial No. 814,5 18.

electric circuit. 1 Y

r The device comprises a circular or curvedtube 2, preferably made ofinsulating ma-' terial, and which is preferably closed at the ends, asbythe plugs 3, of insulating material. Arranged in the tube. and extendinglongitudinally thereof is a wire or con-- ducting element 4, ofrelatively low resistance, one end of which extends through the plug atthe end of the tube. Disposed within the'tube and spaced from theconducting element 4, is a relatively high resistance element 5, whichis substantially parallelto the wire 4. The high resistance element 5'ispreferably connected at its endsand within the tube with wires 6 and 7of low resistance, such as iron wires, and these wires extend throughtheplugs at the ends of the tube. Disposed in the tube and formingcontact with the conductor 4 and the resistance element 5., is a rollingcontact device, which maybe a steel ball, but which is preferably a dropof mercuryS.

mercury varies, thereby varying the amount of resistance in circuit, andthis resistance can beadjusted very closely by a careful turning of thecurved tube. 1

In the drawings I have shown the tube as,

being circular in form and have provided means so that the tube may beturned on the iron wire 6 extends into thetube so that the mercury cancontact with the wire, thereby cutting out all resistance when desired.

The tube is preferably seated in an annular groove 13 formed in a knob 9of bakelite or other comparable material, and the knob is providedwith'an axially disposed stem 14: which projects through a panel 15 orother supporting element. By rotating the knob,

the position of the tube is shifted and the mercury flows to a differentposition, varying the resistance. The rotation is limited by a stop 16on the back of the knob which engages a projection or stop 17 on thepanel.-

the resistance of an By turning orrocking the curved tube, the positionof the v I fsmmc'am of Letters Patent- P t ted J n 8, 1920,

have obtained excellent results employing a resistance elementconsisting of a piece of cotton or other fabric, cord or string, soakedin a mixture which when dry has a high re sistance. For this purpose Ihave employed a mixture of hot glue and lamp black, in which the stringis soaked and then dried. This resistance element possesses manyadvantageous features. It is more or less flexible and will not breakdue to expansion or contraction or shocks, and is much more durable thanrigid carbon resistance elements which have heretofore been largelyused.

I claim I 1. A variable resistance device,-c0mprising a curved tube, aconducting element in saidvtube, a resistance element in said tubeinsulated from and disposed in substantial parallelism with saidelement, and a rolling contact engaging said conducting element andresistance element.

2. A variable resistance device, comprissistance element.

4. A variable resistance device comprising a circularly bent tube ofinsulatlng material closed at the ends, a conducting element disposedwithin said tube and extending longitudinally thereof,'a resistanceelement in said tube in substantial parallelism with said conductingelement, a rolling contact in said tube contacting with said conductingelement and said resistance element, and a mount for said tube wherebysaid tube may be turned about its axis to cause said contact to roll.

5. A variable resistance device comprising a curved tube, a conductingelement disposed longitudinally in said tube, a fabric stringimpregnated with resistance material disposed in said tube insubstantial parallelism with said element and insulated there from, andadrop of mercury in the tube making contact with the element and thestring.

6. A variable resistance device comprising a curved tube of insulatingmaterial closed at the ends, a conducting element disposedlongitudinally in said tube, a resistance element in said tube spacedfrom and in substantial parallelism with said conducting element, a dropof mercury in said tube contacting with said elements, a mount in whichsaid tube is arranged and a stem on said mount for supporting the mountand about the axis of which the mount is adapted to be rogated to causethe mercury to roll in the in e.

' In testimony whereof, I have hereunto set my hand at San Francisco,California, this 23rd day of July, 1919.

JOHN PARKIN, JR.

. n presence oflV. W. HEALEY, C. S. EVANS,

